Numerous sensors or detectors exist for sensing and providing an indication of some particular phenomenon. Though the types of phenomena being detected may vary greatly, various broad categories of sensors may be perceived. For instance, the output provided by many types of sensors is an electrical signal, and it is to this class of sensor that the present invention pertains.
Within the broad class of sensors which provide an output signal of electrical character, there are some which are capable of generating the electrical signal solely as a result of the phenomenon being sensed. Such sensors might be electrochemical in nature, or may employ a bimetal to generate an electrical signal or, still further, may use a magnetic interaction for generating a signal potential. On the other hand, another type of sensor requires at least some active electronic circuitry to provide the basic output signal and accordingly, relies upon an external source of electrical power or voltage to supply the circuitry internal to the sensor. It is with this latter class of sensor that the present invention is concerned.
Typically, for a sensor incorporating circuitry requiring an external power source, there will be required three conductive leads or wires for connecting the sensor with a subsequent use (or load) device. One wire is typically responsible for supplying the operating potential to the sensor; another wire is responsible for conveying the output signal from the sensor to the load or use circuitry; and the third conductor is responsible for providing a reference potential relative to the operating potential and also with respect to the output signal. Examples of such three-wired sensors may be found in each of the aforementioned applications, U.S. Ser. No. 07/240,782 (HCI-386) and U.S. Ser. No. 07/240,783 (HCI-387), to which reference may be made and which are incorporated herein by reference. The sensors of those applications are intended to measure wheel speed, as in an anti-lock braking system.
In certain applications of sensors of the type requiring an external supply of electrical power, there may be relatively little room available for the running of three wires between the sensor and the load circuit to which it is connected. Moreover, in instances in which conductive wires must be run between the sensor and the load circuit, the opportunity for difficulty in the respective connections between circuits is increased by the number of conductors required. Still further, the cost of each conductor wire and associated connector terminals may be a significant part of the cost of the sensor assembly.
Accordingly, it is a principal object of the invention to provide, for a sensor requiring an external electrical power source, an arrangement employing fewer than three conductors for connecting the sensor with a load circuit.
It is a further object of the present invention to provide a sensor, and particularly a speed sensor, having improved circuitry for providing electrical power thereto and an output therefrom to a load circuit. Included in this object is the provision of input circuitry associated with the load circuit adapted to support the foregoing objects.